Technological development and increased demand for mobile equipment have led to a sharp rise in the demand for secondary batteries as energy sources. Among these secondary batteries, lithium secondary batteries having high energy density and high operating voltage, long cycle lifespan and low self-discharge are commercially available and widely used.
In addition, increased interest in environmental issues has brought about a great deal of research associated with electric vehicles (EVs), hybrid electric vehicles (HEVs) and the like as alternatives to vehicles using fossil fuels such as gasoline vehicles and diesel vehicles which are major causes of air pollution. Nickel-metal hydride (Ni-MH) secondary batteries are generally used as power sources of electric vehicles (EVs) and hybrid electric vehicles (HEVs). However, a great deal of study associated with use of lithium secondary batteries with high energy density, discharge voltage and power stability is currently underway and some of such lithium secondary batteries are commercially available.
A lithium secondary battery has a structure in which a non-aqueous electrolyte comprising a lithium salt is impregnated into an electrode assembly comprising a cathode and an anode, each comprising an active material coated on a current collector, and a porous separator interposed therebetween.
In general, when HF is present in a lithium secondary battery, the moisture decomposes into hydrogen gas during charge and discharge. As a result, a swelling phenomenon occurs. Furthermore, in serious cases, explosion may occur. In addition, HF may cause corrosion of an electrode due to its acidity.
Accordingly, there is an increasing need for methods of removing HF present in the battery.